1. Field of the Invention
The invention relates to a one-way valve for delivering a viscous product from a container or retaining it in said container.
2. Description of the Prior Art
A valve of the abovementioned type has already been proposed, e.g. in FR-A-2 373 740, said valve having a partially elastic element serving as a flap, which, on the one hand, in its rigid part, is fixed to the container by a hooking means, and, on the other hand, in its elastic part, bears elastically against a sealing zone integral with the container. A valve of this kind is used in particular to prevent any secondary air in flexible tubes containing pasty or viscous products, such as toothpastes. It is known that tubes of this type usually consist of a tubular body of generally circular or elliptical section. One end of the said tubular body is closed after filling of the tube by flattening and welding. At the other end, a head or connector forming the neck of the container is connected to the tubular body.
When a certain quantity of the product is expelled from an elastic tube that can be flattened, the tube, by virtue of its elasticity, tends to resume its initial shape when the expulsion pressure ceases and in so doing tends to draw in air in place of the expelled product. This forms a disadvantage for some types of product for which the presence of air before they are expelled has a detrimental effect. The presence of air, particularly finely divided air, in some toothpastes can cause the separation of liquid and solid phases or drying-out of the paste. Moreover, the presence of air can cause oxidation of certain flavouring oils used in toothpastes. In the case of perfumed creams, the presence of air can cause oxidation of some of the compounds forming the perfumes.
A valve of this kind is described in the aforesaid document FR-A-2 373 740. However, the latter only displays advantageous operation to the extent that the pressure exerted by the elastic part is strong enough to drive back the viscous product when the expulsion pressure ceases, meaning that each valve must be adapted to the viscosity of the product.